Process for producing lustrous cellulosic products



Patented Aug. 7, 1951 UNITED STATES PATENT OFFICE PROCESS FOR PRODUCINGLUSTROUS CELLULOSIC PRODUCTS Joseph Hendrickson Balthis, Wilmington,DeL,

and Frank Kerr Signaigo, Kenmore, N. Y., assignors to E. I. du Pont deNemours & Company, Wilmington, Del., a corporation of Delaware NoDrawing. Application August 22, 1946, Serial No. 692,386

9 Claims. (Cl. 117-102) This invention relates to cellulosic materialsof reduced flammability, and more particularly to the production ofimproved films, fibers, and fabrics of cellulose and its derivativeswhich are lustrous yet contain substantial quantities of insolubletitanium compounds.

It is well-known that the flammability of cellulosic materials may bereduced by incorporating suitable organic or inorganic materialstherein. Though water-soluble impregnants suffice for some purposes,insolubility in water is frequently required. Water-insoluble compoundsare usually incorporated by impregnating the cellulosic material with awater-soluble compound of an element which is subsequently precipitatedin the form of one of its insoluble compounds, for example, as an oxide,silicate, phosphate, or tungstate. Titanium compounds have been founduseful for this purpose but their utility has been limited by attendant,undesired delustering of the impregnated material. This ability oftitanium compounds to deluster is well known and it is possible at timesto take advantage of it. Thus, many textile materials are delustered byintroducing titanium compounds before or after spinning. For manypurposes, however, the luster and transparency of cellulosic materialsmust be preserved. Brightness and luster are frequently required intextile materials and to an even greater extent in films and foils. Manytitanium compounds are free from color, chemically inert, difficultlysoluble, and non-flammable, all of which-make them attractive asflame-retarding agents provided they can be incorporated in substantialquantity without delustering the cellulosic material. One principalobject of this invention therefore is to provide methods by whichtitanium may be incorporated in films, fibers, and fabrics of celluloseand its derivatives without incurring undesired delustering of suchmaterials.

In accordance with this invention, lustrous films, fibers, and fabricsof regenerated cellulose and cellulose esters and others containingtitanium are produced by suitably impregnating such cellulosic materialswith a soluble titanium compound, removing superficial impregnant fromthe treated product under non-hydrolyzing conditions, and thenprecipitating a water-insoluble titanium compound within impregnatedcellulosic material.

In a more specific and preferred embodiment, the invention comprisesproducing a lustrous regenerated cellulosic material of materiallyreduced flammability containing at least 3% by weight of titanium, byimpregnating said material with a relatively concentrated solution of awater-soluble, inorganic compound of titanium such as titanyl sulfate,removing excess or superficial impregnant from the treated material bythoroughly rinsing under non-hydrolyzing conditions and in the presenceof an alcohol, and then precipitating a water-insoluble titaniumcompound Within the rinsed cellulosic product.

Regenerated cellulose and its derivatives have an appreciable tendencyto incorporate titanium when immersed in solutions of titaniumcompounds. The amount incorporated depends upon many factors, includingthe nature of the solvent, the activity of the titanium compound, theprevailing temperature, the time of impregnation, and the chemicalcomposition and degree of swelling and orientation of the cellulosicmaterial. The choice of impregnating conditions and the particulartitanium compounds introduced and precipitated depend upon the type ofcellulosic material and the use for which it is intended. The presentinvention is not limited to any particular method of impregnation orprecipitation though, by Way of illustration, certain expeditious andmore preferred procedures will be described.

In accordance with one adaptation of the invention, regeneratedcellulosic yarn or fabric is suitably impregnated by immersion,preferably, in a titanyl sulfate solution containing from about 50 to150 g./l. of T102 for a relatively short period of time and at roomtemperature or temperatures ranging from 0 C. to C., care beingexercised not to utilize elevated temperatures at which hydrolysis wouldoccur. After such impregnation, excess impregnant is removed asthoroughly as possible by conventional hydro-extraction, draining orwringing. These and similarmechanical operations are insufiicient inthemselves, however, to prevent undesired delustering of the cellulosicmaterial in the subsequent operations necessary to insolubilize or fixthe titanium. When materials treated in this manner are immersed inaqueous alkali, phosphate solution, water at ordinary temperature, orother media for fixing the titanium, external precipitation occurs inthe bath as well as internal precipitation within the cellulosicmaterial. The cellulosic material becomes coated with a rough, adherent,delustering deposit of titanium compound. This deposit is relativelyeasy to remove from films but is exceedingly difficult, if notaltogether impossible, to remove from textile materials by washing.Seemingly the deposition is due to incomplete removal of impregnatingagent from the surface of the cellulosic material prior to fixation ofthe titanium. To overcome this and avoid such deposition, a thoroughrinsing of the impregnated material in preferably an alcohol or anaqueous alcohol is resorted to. Ethyl alcohol is particularly preferredfor use since it does not extract titanium yet appearsto be compatiblewith aqueous titanyl sulfate in all proportions, even though solidtitanyl sulfate, TiOSO4.2I-IzO, is substantially insoluble therein. Therinsed product can then be washed with water torender it sulfate free,but preferably it is treated with a suitable neutralizing agent, such asa 3% solution of sodium carbonate, followed by'water washing.

To a clearer understanding of the invention, the following specificexamples thereof. are given. These are merely illustrative and are notto be construed as in limitation of the invention:

Example I Five skeins of regenerated, freshly-spun, hightenacity gelrayon (275 denier, 120 filaments) yarn areimpregnatedby immersion atroom temperature for one minute in a titanium solution obtained bydissolving 613 parts of essentially acid-freev titanyl sulfate: of theapproximate. for-- mula, TiOSO42I-I2O, in. 625 parts ofwater,.filtering: and adding water' to adjust its titaniumconcentrationto. 150grams/literof T102. The titanium-treated. skeins: are.hydro-extracted. and

then finished for comparative purposes by; the

following procedures inwhich (a) and. (b) com,- prise; orthodox.finishing and. (c), (d). and (e) areinaccordance with thisinvention:

(a) One. skein is. immersed in aqueous alkali. Even though the yarn. hasbeenhyro-extracted, hydrous titaniaprecipitates. on. the surface of theyarn andin the solution. The precipitatedtitania adheres. tenaciously'tothe yarn as a. delustering' depositof titania. and is not completelyremoved; by; washing. The .dry'delustered yarn contains 1.9%. Tibyweight. Aggregates oftitaniumoxide adhering: to individual filamentscan. be. detectedmicroscopically.

(b), Thesecond skeinissimply washed inpwater: at room temperature (about25 C.) until free of.

sulfate. Titania precipitates in. the form. of a delustering deposit onthe surface of theyarn, and. the final yarn, which contains about 1.3%Ti by weight, is .delustered and harsh.

(c) The third skein is thoroughly rinsed. in 95% alcohol to removesuperficial titanylsulfate, hydro-extracted, immersed in l sodiumhydroxide-and washed with water until alkali-free. In contrast to skeins(a') and (b) there is no: visible titania precipitation and the yarn,which contains about 1.6% titanium by weight; is bright and lustrous.

(d) The fourth skein is immersed for five minutes in water containing 1sodiumhydroxideand 5% mannitol by Weight and is then washed with wateruntil free of alkali. There is no external precipitation of, titania andthe lustrous product contains about.l'.1% titanium by weight. (e) Thefifthskein is cooled to 0-l0 C. and rinsed in water previously cooled tothis'same temperature. The yarn is then neutralized at normaltemperature by treatment with 3% sodium carbonate solution and is washedwith water until neutral. As in the. instances of (c) and (11) above; noexternal precipitation of titania is evident and the yarn is a lustrousproduct.

Example II Freshly-spun rayon yarn is washed, desulfured, bleached, and.treated as. hereinafter described while still in the swollen gel state.Titanyl sulfate solution; is prepared in the manner described in ExampleI, but its titanium. content is adjusted to 134 grams/liter of T102 and21.5% more Hz'SOrwater.. The titanated yarn is soft and lustrous incontrast to the material resulting from the orthodox treatment of (a)above.

(0) A third portion of the impregnated yarn is passed through a watersolution containing 1% NaOH' and 10% glycerol by weight and is washed inwater. The titanium-containing yarn is-alsosoft and lustrous.

Example III A skein of; a. cellulose derivative, hydroxyethyl cellulose,yarn is immersed: in titanyl' sulfate; solution (150 grams/liter-ofT102). for fifteen minutes, removed, allowedto drain, thoroughly rinsedin. 95% aqueous ethyl alcohol, soaked in.3-%.aqueous= NazCOs. solution,and water washed. The. soft.

bright. lustrous product contains. 16.4%. titanium by weight.

Example IV Carboxyethyl. cellulose yarn. CHzCHzCOOH per glucose unit;preparedby the reaction of alkali cellulosewith acrylonitrilefolilowedby hydrolysis) is treated asv in Example III-L The. treated.yarn. is. lustrous. and contains. about 9% titanium. by weight.

Example V" Cellulose yarn, modified with. by weight.

of a saponified copolymer. of allylidene. diacetate. and. vinyl.acetate, is treated in themanner described in Example III. The lustrousproduct containsabout. 7% titanium by weight.

Example VI A solution. of titanyl sulfate containing the. equivalent of12 parts by weight. of 'IiOz is pre-- pared by dissolving 29.4- parts byweight of. TiOSOaZI-IzO in 70.6 parts. of. water. Freshly cast films of.regenerated cellulose are soaked: in the solution at room temperature.for. 15 min utes and finished asfollows: Thefilm is removedfromthe'titanyl sulfate and immersed in aqueous ammonia, av copiousprecipitate of hydrous titania formingin the ammoniacal solution andsome of the'precipitate adhering to the. film. In contrast to resultswith fibers and. fabrics, the precipitate may be removed'by rubbing orwashing in water. To. prevent precipitation altogether,

the impregnated film is'rinsed with alcohol prior to immersion in theaqueous ammonia. Following. such ammonia treatment, the. film is washedin water until free of sulfate. The films contain up to 18-20% by weightof titanium, are clear, transparent and lustrous, and can be softenedwith. glycerol. or. other known softening agents. The introduction of.titanium. reduces solubility in cuprammonium hydroxide and. impartsopacity to. ultra-violet light.

Although the invention has been. described above as applied to. certain.preferred. embodiments thereof, it will be obvious that due variance(0.5. mol of.

therefrom may be made without departing from its underlying principlesand scope. Thus, although it is particularly applicable to the treatmentof textile materials such as cellulosic threads, yarns, or fabrics, theinvention is not limited thereto. It may, for example, be applied tofilms, foils, sheets and even to plastic compositions and moldedobjects. The materials treated may consist of or contain celluloseacetate or other derivatives of cellulose, for example, cellulosenitrate, cellulose nitro-acetate, cellulose formate, cellulosepropionate, cellulose butyrate, hydroxyethyl cellulose, ethyl celluloseand other esters, ethers, and ester-ethers of cellulose. The titaniummay be introduced during spinning or casting, as for example byincorporating titanyl sulfate in an acid regenerating bath, or at anysuitable stage during subsequent processing or fabrication.

It is usually possible to introduce up to 20% by weight of titanium(calculated as TiOz) into films and up to 13% by weight into textilematerials. The amount of titanium introduced may be relatively small, e.g., as low as .5% by weight. At least 3 by weight of titanium isrequired to materially reduce flammability. The reduction inflammability is directly related to the quantity of titanium introducedand larger quantities (preferably from 5-10% by Weight) are frequentlydesirable when the cellulosic material has a large surface area, as inthe case of brushed rayon fabrics. Preferably, also, the titanium isprecipitated within the cellulose structure as the oxide, phosphate, orphytate.

As noted above, titanyl sulfate is advantageously employed as thepreferred impregnating agent by virtue of its high solubility in water,its relatively non-injurious effect on cellulose, and its ability tointroduce large quantities of titanium. It is usually employed inaqueous solutions at a concentration equivalent to, say, from 50 to 150gram/liter of TiOz, though higher concentrations (up to 200 or 300g./l.) can also be used, i. e., from 5%-30% TiOz in solution. Excesssulfuric acid above that required for stoichiometric equivalence withtitanyl ion sometimes facilitates introduction of the titanium thoughless than 100% excess is preferred.

The soluble titanium compound may be incorporated in a variety of ways,as for example by a bath treatment, by padding or by spraying. It is notalways imperative that impregnation with titanium be the first step andsuch impregnation may be preceded by introduction of phosphate or otheranion required to fix the titanium in insoluble form. Any solubletitanic, titanous, or titanyl salt may be used though the sulfates,chlorides, oxalates, and acetates are particularly suitable. Thetitanium may be precipitated within the fibers by a variety of agents,for example, phosphates, phytates, silicates, tannates, borates, etc.Though water is preferred as the impregnating and precipitating medium,all or part of the water may be replaced with alcohols, acetone,dioxane, and the like.

It is not essential to pre-swell the cellulosic structure but this isusually helpful and may be accomplished by soaking in Water or otherswelling medium or, in the case of regenerated cellulose, by employingso-called gel cellulose which has not been dried after regeneration. Therate of incorporation of titanium may sometimes be increased by raisingthe temperature of the impregnating solution, but, as already noted,care must be exercised to avoid hydrolysis. The time of impregnation mayvary from a few seconds to aminute or more in case of yarns, fabrics,and

films continuously passed through an impregnating bath up to 15 minutesor longer in batchwise impregnations.

The alcohol rinsing step may be carried out at any convenienttemperature and pressure, though operation at or near room temperatureis generally expedient. While ethyl alcohol comprises a preferredreagent for use in this step, other watersoluble monohydric orpolyhydric alcohols, for example, methyl alcohol, propyl alcohol,ethylene glycol, glycerol, or glucose, may also be used or substitutedfor ethyl alcohol. It is usually possible to reduce the cost of thealcohol without seriously impairing its effectiveness by diluting itwith water.

Optionally, an aqueous solution containing both an alkali and apolyhydric alcohol, for example, 1% sodium hydroxide and 10% glycerol byweight, may be substituted for the alcohol. There is no precipitationwhen a large volume of such solution is used through titanium oxide isimmediately precipitated by alkali in the absence of glycerol. Aqueoussodium hydroxide-glycerol tends to extract titanium, hence time thereinis held at a minimum, usually 15 minutes or less.

Water at low (ice-cold) temperature can be used in lieu of alcohol orpolyhydric alcoholalkali. It is imperative, however, that thetemperature of the water not exceed about 10 .C. If the temperature ofthe water is higher, hydrolysis occurs with ensuing undesiredprecipitation of titania and delustering of the cellulose. The rate ofhydrolysis of titanyl sulfate is markedly dependent upon temperature.Under conditions at which precipitation (hydrolysis) is immediate at 250., it is inhibited for about two hours at 2 C. Like ethyl alcohol,water has little or no tendency to extract titanium from impregnatedmaterial, though both extract sulfate ion slowly. There is noprecipitation of titania in adequately cooled water. Advantageously thecellulosic material may be precooled prior to treatment to a temperatureranging from 0 C.- 10 C.

When rinsing with polyhydric alcohol-alkali, temperature and pressureare not particularly critical. It is possible to use many polyhydricalcohols, for example, ethylene glycol, glycerol, mannitol or glucose,and even, at times, monohydric alcohols. Likewise, a variety of alkalinematerials may be used including alkali (sodium, potassium, etc.) andalkaline earth metal (calcium, barium, strontium) hydroxides andcarbonates and ammonium hydroxide. Both the absolute concentration andthe relative pro-portions of polyhydric alcohol and alkali may be variedwidely.

Processing subsequent to rinsing depends upon the particular titaniumcompound to be precipitated. If titanium oxide is to be precipitated,the especially rinsed materials are simply washed with water untilsulfate-free or, since this is slow, neutralized with alkali, preferably3% aqueous sodium carbonate, and washed with water. If it is desired toprecipitate another insoluble titanium compound, the rinsed ma terialmay be immersed in a dilute solution of the desired anion, as, forexample, a water'solution containing a phosphate, a phytate, or thecorresponding free acids. Acids which extract titanium, for example,hydrochloric and sulfuric, should be avoided.

It is usually advantageous to employ aqueous sodiumbarbonate asaneutralizing agent and to avoidan acid rinse in removing the carbonate.An acetic acid rinse subsequent to sodium carbonate; treatment, eventhough followed by thorough washing in water, frequently acceleratesthe; deterioration of titanium-containing cellulose materials atelevated temperature.

If; desired; the process may be used to reduce the flammability ofpreviously delustered materials when it is desirable to avoid furtherreduction in luster, clarity, or surface deposition of inorganicmaterial.

We claim as. our invention:

1. A. process for producing a lustrous regenera'tedcellulosic productwhich comprises impregnating" a regenerated cellulosic material with awater-soluble titanium compound, removing superficial impregnanttherefrom by thoroughly rinsingwith a solution of astraight chainwatersoluble aliphatic alcohol, and then precipitating a delusteringconcentration of a water-insoluble titaniumcompound ranging from 3% to20% of titanium by weight within the rinsed cellulosic materialbyreacting said first-mentioned titanium compound with an alkalineprecipitating agent.

2. A process for producing a lustrous regen erated cellulosic productwhich comprises impregnating said cellulosic material-with awatersoluble titanium compound, removing superficial impregnanttherefrom by thorough rinsing with water containing a straight chain,water-soluble aliphatic alcohol, and then precipitating awater-insoluble titanium compound in amount ranging from 3%-20% titaniumby weight within the rinsed cellulosic material by treating saidmaterialwith a solution of an alkaline precipitating agent. a

3. A process for producing a lustrous regenerated cellulosic productwhich comprises impregnating said cellulosic material with awatersoluble titanium compound, removing superficial impregnanttherefrom by thoroughly rinsing with an aqueous alkali and water-solublestraight chain, aliphatic polyhydric-alcohol solution, and thenprecipitating a water-insoluble titanium compound in amount ranging from3%-20% by Weight of titanium within the rinsed cellulosic material bytreating said material with a solution of an alkaline precipitatingagent.

4. A method for producing a lustrous regenerated cellulosic product,comprising impregnating a regenerated cellulosic material with asolution. of. titanyl sulfate, removing superficial impregnant from thesurface of the resulting product by rinsing said product in aqueousethyl alcohol, and then precipitating a delustering concentration of aninsoluble titanium compound in amount ranging from 5%-10% by weight oftitanium within the resulting alcohol-rinsed product by treatment withan alkaline precipitating solution.

. 5. A method for producing a lustrous regenerated cellulosic materialwhich comprises initially impregnating said material with a solution oftitanyl sulfate, removing superficial impregnant from the surface of theresulting product bythoroughly rinsing it with an aqueous solution ofsodium hydroxide and glycerol, and then neutralizing the rinsed productwith an alkaline solution to precipitate therein an insoluble titaniumcompound in amount ranging from 5l0% by'weightof titanium. v

6. A method for producing a lustrous regeneratedcellulosic product ofreduced. flammability which corn-prises immersing the. regeneratedceblulosic material in a concentrated titanyl sulfate solution toimpregnate the same, following such.

titanium compound, ranging from 3%-20%- by weight of titanium within therinsed cellulosic product by treating itwith an alkaline precipitatingagent.

7. A method for producing a lustrous regen-- i erated cellulosicproduct'of reduced flammability which comprises impregnating theregenerated cellulosic material by immersion in a concentrated titanylsulfate solution containing from -150 g./l. T102 at temperatures rangingfrom 0 C. to 80 (3., following such impregnation thoroughly rinsing theimpregnated product with a solution of a water-soluble straight chainaliphatic alcohol to remove excess impregnant from its surfaces, andthen precipitating a delustering, concentration of a Water-insolubletitanium compound ranging from 5% to 10% by weight of titanium withinthe rinsed cellulosic product by treating said product with a dilutesolution of sodium carbonate.

8. A method for producing a lustrous regenerated cellulosic yarn ofreduced flammability which comprises impregnating the regeneratedcellulosic material by immersion in. a concentrated titanyl sulfatesolution, following such impregnation'thoroughly rinsing said materialwith ethyl alcohol to remove superficial impregnant from its surfacesand-then precipitating a de1ustering concentration of a water insolubletitanium compound ranging from 5l0% by weight of titanium within therinsed cellulosic product by treating said product. withan alkalineprecipitating agent.

9. A process for producing a lustrous, regenerated cellulosic productwhich comprises impregnating said cellulosic material with an aqueoussolution of a titanium compound, removing superficial impregnant fromits surface by thoroughly rinsing it with a liquid reagent containing astraight chain, water-soluble, aliphatic alcohol and without hydrolysisof said titanium compound taking place, and thereafter precipitating adelustering concentration of a water-insoluble titanium compound rangingfrom 3% to 20% by weight of titanium within said impregnated cellulosicmaterial by reacting the titanium compound impregnant with an alkalineprecipitating agent.

JOSEPH HENDRICKSON BALTHIS. FRANK KERR SIGNAIGO.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS

1. A PROCESS FOR PRODUCING A LUSTROUS REGENERATED CELLULOSIC PRODUCTWHICH COMPRISES IMPREGNATING A REGENERATED CELLULOSIC MATERIAL WITH AWATER-SOLUBLE TITANIUM COMPOUND, REMOVING SUPERFICIAL IMPREGNANTTHEREFROM BY THOROUGHLY RINSING WITH A SOLUTION OF A STRAIGHT CHAINWATERSOLUBLE ALIPHATIC ALCOHOL, AND THEN PRECIPITATING A DELUSTERINGCONCENTRATION OF A WATER-INSOLUBLE TITANIUM COMPOUND RANGING FROM 3% TO20% OF TITANIUM BY WEIGHT WITHIN THE RINSED CELLULOSIC MATERIAL BYREACTING SAID FIRST-MENTIONED TITANIUM COMPOUND WITH AN ALKALINEPRECIPITATING AGENT.